In particular, the present disclosure relates to the field of surface treatment of dielectric polymeric materials with shaped and/or grooved polymeric surfaces, the treatment of surfaces with embedded inorganic particles, or the treatment of dielectric polymer composites with inorganic particulate or fiber fillers. Charge dissipative surface properties are needed for polymer-born devices, such as external spacecraft or solar arrays components, for instance, Flat Cable Conductors (FCCs) with long-term durability of this charge dissipation and other functional properties in GEO space, or polymeric composites-based materials and devices with long-term durability of this charge dissipation in GEO space and in other extreme environments.
Ion bombardment of polymers is widely used in the electronic and other device manufacturing industry, mostly for photo-resists stripping in microelectronics, ion implantation of polymers for optical waveguides formation, plasma surface treatment to enhance adhesion of metals deposited on polymers and printability improvements, polymers' micro-hardness increase, etc. In many cases the medium- or high-dose ion bombardment of a dielectric polymer is causing surface cross-linking or chain destruction due to energy transfer at atomic collisions, as well as surface carbonization. Change of many surface properties have been found to be associated with the compositional, structural, and, quite often, morphological surface transformations due to ion bombardment and selective sputtering of the polymers surfaces in vacuum. Some surface reduction due to ion beams sputtering, gaseous atoms migration with the formation of volatile final products and their release from the surface of the polymers in vacuum, i.e. surface depletion of final gaseous products, and, finally, surface carbon content increase (in the bombarded region), as well as simultaneous and subsequent surface structural reconstruction is called “surface carbonization”. Significant change of mechanical and optical or electrical properties, such as surface hardness, wear resistance, oxidation resistance, and electrical surface conductivity, provided in a wide range of values and wide temperature range, may be achieved by ion beam treatments of polymers [See References 1-5].
It is important to mention, that all the studies of surface conductivity, or surface charge dissipation of dielectric polymers, provided by ion beam treatments, have been done on flat, or, to say, planar polymer films, synthesized specifically for the treatment experiments or produced industrially.
Not just advanced space polymer films in various space applications, but also polymer-based products, for instance, such as Flat Cable Conductors (FCCs) that are used as connections between panels on solar arrays in geosynchronous (GEO) orbits, would strongly benefit from providing charge dissipation to its both external surfaces, to prevent the charge collection, arcing and associated damage under radiation environment, especially when to be used in nowadays long-term space missions. However, manufacturing the products for such applications with charge dissipating surface properties might present difficulties.
The FCCs are manufactured in different sizes and shapes, based, for instance, on DuPont Pyralux LF1010, that basically consists of a Pyralux LF1010 copper clad laminate and same type coverlay, i.e. Kapton100HN (1 mil) films, joined together by a special temperature sensitive acrylic adhesive with thin copper strips pressed in between them at processing stages, and the Cu foil strips ending in electrical contacts outside the made structures [6]. Therefore, in FCCs 100 (FIGS. 1 and 2) the dielectric polymeric front and back films do not represent a flat, plain surface, but rather have repeatedly shaped, or, to say, “grooved” surfaces 102, 202, as can be seen in FIG. 1 for the front surface 101 and FIG. 2 for the back surface 201. Since the ion beam treatment is of a line-of-site nature, with quite strong angular dependence of sputtering rate, this surface relief may influence the uniformity and effectiveness of any ion beam treatment, causing shadowing of the ion beam by the walls of formed grooves.
Another critical difference in treatment of real FCC structures is the condition of the back surface. In comparison with a shiny and smooth front FCC surface, the back surfaces were found to be rough and, with small inorganic particles embedded randomly throughout the surface which comes as a result of the specific technological process of manufacturing of the FCCs. The surfaces of FCC units have been characterized extensively by SEM/EDS (Scanning Electron Microscopy/Energy-Dispersive x-ray Spectroscopy) methods. Front (FIG. 3a and FIG. 3b) and back (FIG. 4a) surfaces SEM images 300, 400 with various levels of magnification, combined with elemental composition studies by EDS, have been used for comparative study of the front and back surface morphology and composition of FCCs from a few manufacturing FCC sets. The part of the front side of the FCCs on top of the Cu strips had a shiny flat surface (see FIG. 1). The plain parts of front FCCs surfaces fully resembled Kapton HN surface, as analyzed by both SEM and EDS. Small inclusion particles that could only be detected under high magnification, are calcium phosphate (Ca3(PO4)2) particles. They are an essential additive in the Kapton HN manufacturing process in order to reduce handling problems due to electrostatic interaction.
Highly developed surface morphology became clearly evident upon the inspection of the back surface, as shown in FIG. 4a that represent the “back side” surface under high magnification. The back surface looks strongly damaged, and it can be clearly seen in FIG. 4a that significant numbers of tiny, mostly submicron size particles are present in the polymer surface. The elemental composition of these particles can be evaluated by EDS. The detailed elemental composition of these particles corresponds in general to the composition of pumice particles, dust of which is used in the manufacturing process as a water slurry under high pressure to enhance the copper adhesion to special acrylic adhesive used in FCCs production. (Pumice stone is made of the following oxides, according to Indian Granites [8]: 70 to 77 percent silica, 11 to 14 percent alumina, 3 to 5 percent potassium oxide, 3 to 5 percent soda, 1 to 3 percent ferrous oxide, 1 to 2 percent ferric oxide, 0.5 to 1 percent magnesia, less than 0.38 percent titanium oxides, and almost all these elements have been found on the back surface by EDS).